1. Field of the Invention
The present invention relates to an alumina sintered body, a method for manufacturing the alumina sintered body, and a semiconductor manufacturing apparatus member.
2. Description of the Related Art
At the present day, in steps for semiconductor wafers, such as transportation, exposure, film-forming process (chemical vapor deposition method, physical vapor deposition method, sputtering, and the like), microfabrication, cleaning, plasma etching, and dicing, a wafer stage which adsorbs/holds a semiconductor wafer using a coulomb force or a Johnson-Rahbek force is used. As the wafer stage, for example, an electrostatic chuck and a susceptor for applying a high frequency wave may be mentioned. For the wafer stage as described above, a dense sintered body in which a flat plate electrode is embedded is used. For example, in Patent Document 1, the wafer stage is manufactured by the following procedure. That is, one surface of a first alumina sintered body sintered beforehand is polished. Next, an electrode paste is printed on the polished surface. Subsequently, after an aluminum powder is formed on the surface of the first alumina sintered body on which the electrode paste is printed to form an alumina compact, hot-press sintering is performed at 1,400° C. to 1,650° C. to form a second alumina sintered body by sintering the alumina compact, and at the same time, a flat plate electrode is formed by sintering the electrode paste. Next, the surface of the first alumina sintered body opposite to the second alumina sintered body is polished to form a wafer stage surface. As a result, a wafer stage having a diameter of approximately 200 mm can be obtained in which the degree of variation in thickness which indicates the variation in thickness from the wafer stage surface to the flat plate electrode is controlled within 0.50 mm. In the wafer stage obtained as mentioned above, finally, the first alumina sintered body functions as a dielectric layer, the second alumina sintered body functions as a support layer, and the flat plate electrode is embedded between the dielectric layer and the support layer.
When hot-press sintering is performed at 1,400° C. to 1,650° C. after the alumina powder is compacted on the surface of the first alumina sintered body sintered beforehand on which the electrode paste is printed, since the sintering temperature of the alumina compact is high, a slight deformation is generated in the first alumina sintered body in some cases. As measures to suppress the deformation as described above, a decrease in sintering temperature of the alumina compact may be considered. For example, in Patent Document 2, a technique in which an alumina compact is sintered at 900° C. to 1,200° C. has been disclosed. In particular, a compact is formed from a mixed powder containing 90 percent by weight of an alumina powder having an average particle diameter of 5 to 50 nm and 10 percent by weight of magnesia and is then sintered at 900° C. to 1,200° C. in an atmosphere containing water vapor at a partial pressure of 0.7 atoms, so that an alumina sintered body is obtained. The technique to decrease the sintering temperature of an alumina compact is useful when an alumina compact is laminated on the first alumina sintered body and is then sintered as disclosed in Patent Document 1, and in addition to that described above, also in other cases, advantages can be obtained in which since the sintering temperature is low, energy consumption in sintering is small, and manufacturing cost of an alumina sintered body can be reduced.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-343733    [Patent Document 1] Japanese Patent Publication No. 2666744